Microphone-transmitter



(Nb Model.

B. A. BARKALOW & N. CRAWFORD.

' MICROPHONE TRANSMITTER,

No. 571,504. Patented N0v.'1 7, 1896.-

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UNiTnD STATES ATENTH BEIGE.

MICROPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent No. 571,504, dated November17, 1896. Application filed July 31, 1896. Serial No. 601,196. (Nomodel.)

To aZZ whom it may concernr Be it known that we, EDGAR A. BARKALOW andNEHEMIAH CRAWFORD, citizens of the United States, residing at Kokomo, inthe county of Howard and State of Indiana, have invented a new anduseful Microphone-Transmitter, of which the following is aspecification.

This invention relates to microphone or telephone transmitters; and ithas for its object to effect certain improvements in transmitters ofthis character that are operated in connection with a mass of granulesof imperfectly-conducting material which is agitated by the vibratoryaction of the diaphragm under the influence of the sound-waves and isincluded in the battery or primary circuit.

To this end the invention contemplates a new and useful construction oftransmitter which attains the maximum of both delicacy and volume in thereproduction of sound, while at the same time being extremely simple andhaving a comparatively low electrical resistance of the transmittingelement.

With these and other objects in view,which will readily appear as thenature of the invention is better understood, the same consists in thenovel construction and arrangement of parts hereinafter more fullydescribed, illustrated, and claimed.

In the drawing the figure is an enlarged vertical sectional view of amicrophone or telephone transmitter embodying the features ofconstruction contemplated by this invention.

Referringto the drawing, the numeral 1 designates a microphone-box madeof hard rubher or other suitable material and open at its front side.The open front side of the box 1 has fitted thereover the vibratorydiaphragin 2, made of the usual material and clamped in place againstthe edges of the box by the circular metallic cap-plate 3, having aflanged rim 4 embracing the edges of the box 1 and secured thereto bymeans of screws 5 or other suitable fasteners. The front cap -plate 3 ofthe microphone box is provided with an offset portion 6, which permits aperfect freedom of vibration for the diaphragm 2, and at its center thesaid cap-plate 3 is provided with an offstanding threaded neck 7 ,onwhich is dctachably fitted the mouthpiece, 8 of the usual flaring orbell shape. Arranged within the microphonebox 1 in rear of the vibratorydiaphragmQis a stationary or fixedly-positioned cup 9, detachablyclamped to the rear wall or side of the box and through the closed sideof the said cup.- The cup 9 is made of suitable nonconducting materialand is of a Width nearly equaling the space between the rear wall of thebox 1 and the diaphragm 2, and interposed between the annular rim of thecup 9 and the inner side of the vibratory diaphragm 2 is a circularflexible packing-ring11,which not only serves to pack the space betweenthe rim of the cup and the diaphragm, but also serves the importantfunction of a damper or cushion for the diaphragm to prevent excessiveor undue vibration thereof.

The stationary non-conducting cup 9 is closed at its outer side by thevibratory diaphragm 2 and is designed to be entirely filled withgranulated carbon or carbon-dust 12 or an equivalent mass of granulatedimperfectly conducting material. The 'mass of granulated material 12confined within the stationary cup 9 is in direct contact with the innerside of the vibratory diaphragm 2 and is illustrated as entirelysurrounding a carbon pencil or bar 13, fitted in diametrically oppositeand alined openings 14, formed in the walls of the cup 9 atdiametrically opposite points.

The carbon pencil or rod 13 is disposed parallel with the diaphragm andhas connected to one end thereof one of the wireterminals a, connectedwith one of the binding-posts 15, fitted to the rear side of the box 1,and the other binding-post 15 has connected therewith the otherwire-terminal Z), which has a metallic connection with the diaphragm 2at the point 16 to complete the primary or battery circuit, it being ofcourse understood that the binding-posts 15 have the usual primary orbattery circuit wire connections therewith.

While only asingle pencil or rod 13 is illustrated in connection withthe mass of granulated conducting material 12, it will be understoodthat one or more of such pencils might be used and might be only partlysurrounded by the granulated material without varying from the generalprinciples of construction involved in the invention.

111 the operation of the transmitter the mass of granules is agitated bythe vibratory action of the diaphragm under the influence of thesound-waves, whereby the resistance of said mass to the passage of theelectric current is varied correspondingly with the movements of thediaphragm, which causes the requisite variations in the current toreproduce sound.

Changes in the form, proportion, and the minor details of constructionmay be resorted to without departing from the spirit or sacrificing anyof the advantages of this invention.

Having thus described our invention, what we claim, and desire to secureby Letters Patent, is

1. In a 1nicrophone-transmitter, the box, a vibratory diaphragm clampedover the front open side of the box and included in the primary circuit,a non-conducting cup secured within the box in rear of the diaphragm andopen at its front side, a mass of granulated carbon or similar materialentirely filling the cup and confined therein by the diaphragm, which isin direct contact with said material,

and a carbon pencil or rod extending through the cup and having theportion within the cup entirely surrounded by the granulated material,substantially as set forth.

2. In a microphone-transmitter, the box, a vibratory diaphragm arrangedover the open side of the box and included in the primary circuit, anon-conducting cup secured within the box in rear of the diaphragm andprovided with diametrically opposite alined openings, a flexible damperor cushion-ring interposed between the annular rim of the cup and theinner side of the diaphragm, a mass of granulated carbon or similarmaterial arranged within the cup and contacting with the inner side ofthe diaphragm, and a carbon pencil or rod fitted in the oppositeopenings of the cup and surrounded by the said mass of granularmaterial, said pencil or rod being disposed parallel with the diaphragm,substantially as set forth.

In testimony that we claim the foregoing as our own we have heretoaffixed our signatures in the presence of two witnesses.

EDGAR A. BARKALOXV. NEIIEMIAH ORAVVFORD. Witnesses:

JOHN P. HUTCHINGS, J. R. MORGAN.

